Failing as a parent

Why do I feel so guilty that my LO has his first cold 😢 he’s only 8 weeks oh man I feel awful all day I’ve been with him and I can’t help but feel bad! He’s so congested he is having trouble eating obviously he’s so uncomfortable 😭

I have my 2 older girls and my 2 year old had a cough and cold and must of passed it on even though me and my husband did everything possible to keep them away!

I called his dr and nurse said just to keep doing everything we are doing but I feel so bad and I’m worried what if it’s more then a mild cold like rsv I’ve seen so many post of that going around and I’m honestly scared! How do I know if it’s that or he’s getting worst and another thing idk how to check his temp I know rectal temp is best for newborn but I honestly can’t do that, like do I buy a special thermometer?? Please help drop some suggestions

Currently running a humidifier, saline, nose frida and also my dr gave us the ok to use baby Vicks on feet and chest but I read not till 3 months so not sure if I should or not I really want to just bc he’s so miserable and anything to make him feel better?